Method and apparatus for measuring dimensions of a feature of a specimen

Abstract

An electron microscope for measuring a dimension of a feature of a specimen includes a focusing lens for focusing an electron beam onto the specimen and a supplying circuit for supplying an exciting current supplied to the focusing lens. A control circuit controls the supplying circuit to vary the exciting current which is supplied to the focusing lens and obtains dimension data of a feature of the specimen at each of the exciting currents which is supplied to the focusing lens. An actual dimension of the feature is determined based on the obtained dimension data. Further, a profile of the feature may be determined based on the changes observed in the dimension data.

I claim:  
     
       1. An electron microscope for measuring a dimension of a feature of a specimen, comprising: 
       a focusing lens for focusing an electron beam onto the specimen;  
       a supplying circuit for supplying an exciting current supplied to said focusing lens; and  
       a control circuit for controlling said supplying circuit to vary the exciting current which is supplied to said focusing lens, for obtaining dimension data of a feature of the specimen at each of the exciting currents which is supplied to said focusing lens, and for determining an actual dimension of the feature based on the obtained dimension data.  
     
     
       2. The electron microscope according to claim  1 , wherein said control circuit includes a curve fitting means for fitting a curve to the dimension data as a function of focusing lens voltage. 
     
     
       3. The electron microscope according to claim  2 , wherein said control circuit determines the actual dimension based on a maximum/minimum of the curve. 
     
     
       4. The electron microscope according to claim  1 , wherein said control circuit increases or decreases the exciting current supplied to said focusing lens in a series of steps until the dimension data obtained at the most recent step differs from the dimension data obtained at a previous step by less than a predetermined amount. 
     
     
       5. The electron microscope according to claim  4 , wherein said control circuit outputs the dimension data obtained at the most recent step as the actual dimension data. 
     
     
       6. A method for measuring a dimension of a feature of a specimen using an electron microscope having a focusing lens for focusing an electron beam onto a specimen, the method comprising the steps of: 
       varying an exciting current which is supplied to said focusing lens;  
       obtaining dimension data of a feature of the specimen at each of the exciting currents which is supplied to said focusing lens; and  
       determining an actual dimension based on the dimension data.  
     
     
       7. The method according to claim  6 , comprising the further step of fitting a curve to the dimension data as a function of focusing lens voltage, wherein 
       the actual dimension is determined based on a maximum/minimum of the curve.  
     
     
       8. The method according to claim  6 , comprising the further steps of: 
       comparing first dimension data obtained at a first focusing lens voltage with second dimension data obtained at a second focusing lens voltage;  
       increasing or decreasing the first focusing lens voltage value if the first dimension data differs from the second dimension data by more than a predetermined amount.  
     
     
       9. The method according to claim  8 , comprising the further step of: 
       outputting the first dimension data as the actual dimension data if the first dimension data differs from the second dimension data by less than the predetermined amount.  
     
     
       10. The method according to claim  6 , wherein the specimen comprises a semiconductor wafer. 
     
     
       11. A method for measuring a height of a feature of a specimen using an electron microscope having a focusing lens for focusing an electron beam onto a specimen, the method comprising the steps of: 
       varying an exciting current which is supplied to said focusing lens;  
       obtaining dimension data of a feature of the specimen at each of the exciting currents which is supplied to said focusing lens;  
       determining the rate of change of the dimension data; and  
       determining the height of a feature based on the rate of change of the dimension data.  
     
     
       12. The method according to claim  11 , comprising the further step of fitting a curve to the dimension data as a function of focusing lens voltage, wherein 
       the height of the feature is determined based on at least one maximum/minimum of the curve.  
     
     
       13. The method according to claim  11 , comprising the further steps of: 
       comparing first dimension data obtained at a first focusing lens voltage with second dimension data obtained at a second focusing lens voltage;  
       increasing or decreasing the first focusing lens voltage value if the first dimension data differs from the second dimension data by more than a predetermined amount.  
     
     
       14. The method according to claim  13 , comprising the further step of: 
       outputting the first dimension data as the actual dimension data if the first dimension data differs from the second dimension data by less than the predetermined amount.  
     
     
       15. The method according to claim  11 , wherein the specimen comprises a semiconductor wafer. 
     
     
       16. A method for measuring a profile of a feature of a specimen using an electron microscope having a focusing lens for focusing an electron beam onto a specimen, the method comprising the steps of: 
       varying an exciting current which is supplied to said focusing lens;  
       obtaining dimension data of a feature of the specimen at each of the exciting currents which is supplied to said focusing lens;  
       determining the rate of change of the dimension data; and  
       determining the variation in the rate of change.  
     
     
       17. The method according to claim  16 , comprising the further steps of: 
       comparing first dimension data obtained at a first focusing lens voltage with second dimension data obtained at a second focusing lens voltage;  
       increasing or decreasing the first focusing lens voltage value if the first dimension data differs from the second dimension data by more than a predetermined amount.  
     
     
       18. The method according to claim  17 , comprising the further step of: 
       outputting the first dimension data as the actual dimension data if the first dimension data differs from the second dimension data by less than the predetermined amount.  
     
     
       19. The method according to claim  16 , wherein the specimen comprises a semiconductor wafer. 
     
     
       20. A method for measuring a profile of a feature of a specimen, the method comprising the steps of: 
       varying an exciting current supplied to a focusing lens;  
       obtaining dimension data of a feature of the specimen at each of the exciting currents which is supplied to said focusing lens;  
       determining the rate of change of the dimension data; and  
       determining the profile of the feature based on the rate of change of the dimension data.